Centrifugal fan and pump



S. C. DAVIDSON. CENTRIFUGAL rm m0 PUMP. APPLICATION FILED NOY- IT, l9l9- Patented Jan. 18, 1921.

INVENTOR M 4? I v By Attorneys,

yam (Jun/A an improved construction described and 01.31am) DAVIDSON, or BELFAST, mnrnim. onn'rmroenr. FAN AND PUMP.

Specification of Letters Patent.

Patented Jan. 18, 1921.

, Application filed November 1?, 1919. Serial No. 338,458.

To. all w ham it may concern: Be it known that I, SAMUEL CLELAND. DA- vmson, of Belfast, Ireland, a subject of the King. of Great Britain and Ireland, have invented certain new and useful Improvements in Centrifugal Fans andPumps, of,

which the followin is a specification.

This invention 1'5 or pumps (hereinafter referred to as fans wherein the air or gas discharged therefrom (hereinafter referred to as primary air operates inductively on a further volume of air or gas (hereinafter referred to as secondary air) by combining with and impart- 111g motion thereto outside the periphery of the fan wheel, without said secondary air passing into, or through the fan wheel itself.

My herein described invention consists of of the apparatus shown inthe specification of my pending application Serial No. 283,438, renewed on the 18th March 1919 (hereinafter referred to as my previous specification) and may be similarly employed, and for the same or similar purposes as those referred to in said previous specification.

In my improved construction, I now employ a series of fixed guide vanes withinthe air chamber of the casing surrounding. the fan wheel (hereinafter referred to asthe air chamber) whereby the primary air, after being discharged from the periphery of the fan wheel, is subjected to the controlling action of said guide vanes, whiphhave the spaces between them open at their inner edges to said primarylair, and also on the side which faces the main duct, through which the supply of secondary air is drawn into said air chamber, and a third series of openings around the outer circumferenceof the air chamber for discharge of the comhined volume of primary and secondary air,

as hereinafter more narticularlvdescribed,

- whereby the strength ofinduotionset up by motion by inductioncau be arranged the primary air discharge from the fan wheel upon the secondary air is of an enh nc d nd more positive character than obtainable with the arrangement of apparatus as described in my previous specification,

I The volume of rseeondary air thus set in wmav be desired, to be either double or several times greater than the volume of rimary air through the fan whee itself, but of course at a reduced velocity of flow ates to centrifugal fans driving the fan wheel, remain chamber around the rooted stationary therefrom, so 7 unobstructed space for the free rotation of the dischargedprimary alr, to enable it to relativelyto that of the primary air which, by imparting motion to the secondary air, must necessarily lose to an equivalent extent its own initial velocity, in proportion to the volume of secondary air to which it imparts motion. If the speed of the fan be kept constant, the velocity of flow of the primary air, up to its mixture with the secondary air from the spaces between the guide vanes,yas well also as the power for substantially constant, irrespective of the volume of secondary air being dealt with.

In carrying this invention into effect, I usually employ a fan wheel of the multibladc type, such as that described in the specification of previous Letters Patent granted to me, and numbered 662395, but other types of centrifugal fans may be used for impelling the primary air into the air )eriphery of the fan wheel, within which I now introduce a series of fixed and more or less radially diguide vanes, which are preferably arranged tangentially to the periphery of the fan wheel, and as nearly as practicable in line with the discharge flow of primaryair therefrom. The inner edges of these vanes facing the back plate of the fan casing are at a short distance away as to leave an intermediate attain its maximum velocity of flow while passing in front of the discharge spaces between the vanes, and whether the vanes be arranged tangentially thereto, or otherwise.

Said vanes are preferably rectangular at theirouter ends, and thereat extend fully across the space between the front and back rim of the fan wheel casing,to each of which they are firmly attached, and may also be rectangular or curved along their inner edges whichterminatc a short distance from,

the periphery of the fan wheel, but I prefer to make their inwardly facing edges, toward the back of the casing, curved away therefrom beginning from a point near the circumference of the air chamber, these edges then slanting inward to a point near the circumference of the intake end of the fan wheel, so that an unobstructed space is thus provided between the back plate of the fan wheel casing and the said inwardly facing edges of the guide vanes, which thus define a space, the margin of which, as proved by practical investigation, closely approximates to the marginal line of highest velocity of flow of the primary air discharge from the fan wheel.

The body of the guide vanes is preferably extended a short way into the secondary air supply duct between the circumference of its inclosing casing, and a short length of pipe which is centrally located within same, and on the outer surface of which the inner ends of the said extensions of the vanes are attached, the diameter of this pipe being sufficiently greater then that of the fan wheel to allow of free insertion or removal of-the fan wheel through it.

The intermediate spaces between the front edges of the extended portions of the guide vanes are openthe whole way from the surface of said interior pipe out to their attachment to the cylindrical inclosing easing of the secondary-air supply duct. The inflow of the secondary air is thus directed at right angles into the discharge current of primary air from the fan wheel, without its having acquired any rotary motion be fore combining therewith inside the spaces between the guide vanes where the primary air is acting inductively.

' The provision of an unobstructed annular space around and between the back plate of the fan wheel casing and the inwardly facingtedges of the fixed guide vanes, is for the free rotation of the primary air as an annulus around the fan wheel, so that it may attain its highest velocity while passing infront of the discharge spaces around the'outer circumference of the fan casing and past the inward edges of the guide vanes, and may thereby impart its maximum of induction effect firstly to that part of the inflowing secondary air which is nearest to the periphery of the fan wheel, and, as the spaces between the guide vanes gradually increase in area toward the rim of the easing, ample room is thus provided for the additional volume of secondary air subsequently drawn into the discharge current of primary air the whole way out to the discharge openings around the circumference of the air chamber casing, consequently none of the secondaryair can enter, or even touch the fan wheel.

When my improved apparatus is employed for drawing oif corrosive gases, which if passed through a fan wheel having its component parts made of steel or iron Would rapidly corrode the said parts, it is essential that a separate supply of primary air from the atmosphere be conveyed clirectly into the eye of the fan wheel by a separate pipe passing through the secondary air supplyduct, so as to completely isolate the primary air from said corrosive gases,

until after it has passed through, and away from the periphery of the fan wheel.

Accordingly when corrosive gases constitute the secondary air which has to be drawn away by induction, said primary air supply pipe and secondary air supply duct, as well as the fan casing, the fixedv guide vanes and attachments, should all be made of such material as will withstand. the action of the corrosive gases (such for example as lead or Doultonwaro) which material, although unsuitable for use when subjected to high centrifugal action, is nevertheless quite suit able for the construction of the ducts. casing, guide vanes, and possibly other parts, all of which, in this apparatus, are stationary, and, as only ordinary atmospheric air is then passing through the rotatin 'l'an wheel. the induced current of corrosive uses does not come in, contact with, or pass through the fan wheel at all.

In order that the nature of the invention may be clearly understood an example embodying the same will now be described by way of illustration with the aid of the accompanying drawings in which Figure 1 is a front elevation, showing the centrally located fan wheel, and the tangentially arranged induetion guide vanes in the casing around it; Fig. 2 is a cross section through the complete apparatus, showing the fan wheel itself with centrally located short length of primary air supply pipe, and an extended length of pipe leading to it through the secondary air supply duct, and also showing the preferred shape of the interior edges of the fixed guide vanes to provide the necessary unobstructed space between them and the back plate of the easing for the passage of the high velocity air, sons to produce the required induction effect between the fixed guide vanes.

Referring to the drawings in both figures of which the same letter indicates the same part, a fan wheel a, preferably of the multiblade type described in my Patent No. 662395, is mounted adjacent to and concentrio with a primary air supply pipe 7) which may be of any suitable length to reach the source from which the atmospheric air supply is being drawn and which is given a sufficiently larger diameter than that of the fan wheel a to allow of this being freely inserted or withdrawn through the said pipe.

A secondary air supply duct 0 is arranged in the form of an annulus surrounding the primary air supply pipe b,this duct being inclosed between an outer casing g project ing from the front rim 9 of the fan casing and a length of pipe 6' both arranged concentric with the primary air supply pipe I).

The pipe 6' is an extension of the primary air supply pipe 5 and may be mounted on the latter with a sliding fit, the extension I) being of any suitable length to reach the source from which the atmospheric air suppLE is being drawn.

be primary air supply pipe 6 carries upon its outer surface the fixed guide vanes (1 preferably arranged tan entially to the pipe b as clearly shown in 1 which also shows the spacesd between t e fixed guide vanes d.

The intake edges d of the guide vanes are somewhat extended toward the front into g of the secondary air supply duct 0.

The outer portions of the rear edges of the guide vanes d are attached to the outer rim of the back plate f of the fan casing between which plate and the front rim of the said casing the outer rectangular en s of the guide vanes d are firml mounted, while the front portions of the xed guide vanes d are somewhat out down in length to enable these portions to be inserted in and attached to the interior surface of the outer casing g of the secondary air supply duct 0.

In order to form the unobstructed space h between the interior edges d of the guide vanes d, the back plate f of the fan casing, and the periphery of the fan wheel, the said interior edges d of the vanes are first curved away from the back plate f toward the front or intake end of the apparatus and are then carried slantin ly inward so as to meet the periphery of t e rear end of the short pipe constituting the primary air supply pipe. This unobstructed circumferential space it permits of the free rotation of the primary air while at its hi hest velocity immediately on leaving the bla es of the fan wheel a, the interior edges d of the guide vanes d being so shaped preferably as to form the marginal l1ne of highest velocity of flow of the primary air discharge from the fan wheel, as described above. Thus the primary air issuing from the fan wheel is allowed to develop its full centrifugal forcewhile passing in front of the inner and narrowest openings in the spaces d between the guide vanes 11 where the maximum inductive power of the said air is exerted by which the secondary air or gases are carried off without passin into or even touching the fan wheel.

hat I claim and desire to secure by Letters Patent is 1. In a centrifugal fan, the combination with a bladed fan wheel of a primary fluid supply, means for admitting the primary fluid to the fan wheel, a secondary fluid supply, means for admitting and subjecting the secondary fluid to the inductive action of the primary fluid discharged from the fan wheel, a fluid chamber surrounding the fan wheel in which the primary and secondary fluids are commingled before being finally discharged therefrom, and a set of fixed guide vanes arranged in said fluid chamber for controlling the inductive action produced by the primary fluid discharged from the fan wheel upon the secondary fluid.

2. Centrifugal fans as described in claim 1, further characterized in that the fixed guide vanes arranged in the fluid chamber have a portion projecting into the secondary fluid supply duct.

3. Centrifugal fans as described in claim 1, further characterized in that the vanes are formed with an unobstructed space for the fluid between the interior edges of the fixed guide vanes and the back plate of the fan casing around the periphery of the fan Wheel for the purpose set forth.

4. Centrifugal fans as described in claim 3, characterized in that the inner edge of each of the fixed guide vanes is secured upon the outer surface of the primary air supply duct. g

5. Centrifugal fans as described in claim 1, characterized in that the fixed guide vanes are arranged tangentially to the periphery of the fan wheel.

In witness whereof, I have hereunto signed my name in the presence of two subscribing wltnesses.

SAMUEL CLELAND DAVIDSON.

Witnesses:

WILLIAM Psornns BLACK, ROBERT MARTIN. 

